Microfabrication using photolithography techniques has conventionally been performed in producing semiconductor devices. The microfabrication is a method of forming a thin film of a photoresist composition on a substrate such as a silicon wafer, applying active rays such as ultraviolet rays thereon through a mask pattern having semiconductor device patterns, developing the pattern, and etching the substrate such as a silicon wafer using the resulting photoresist pattern as a protection film (mask). With the increasing density of semiconductor devices in recent years, the active rays used have been changed to those at shorter wavelengths, for example, from KrF excimer laser (wavelength of 248 nm) to ArF excimer laser (wavelength of 193 nm).
Accordingly, the effects of diffuse reflection or standing waves of active rays from the substrate have become a serious issue, and a method has been widely adopted in which Bottom Anti-Reflective Coating (BARC) is provided as a resist underlayer film between the photoresist and the substrate for serving the function of preventing reflection.
Known examples of the anti-reflective coatings include: inorganic anti-reflective coatings including, for example, titanium, titanium dioxide, titanium nitride, chromium oxide, carbon, and α-silicon; and organic anti-reflective coatings made from a light absorbing substance and a polymer compound. The former requires equipment for forming films such as a vacuum deposition system, a CVD system, and a sputtering system, whereas the latter requires no special equipment. In this respect, organic anti-reflective coatings are advantageous and have been elaborately examined.
ArF immersion lithography in which exposure is performed through water has been practiced as a next-generation photolithography technique that replaces the photolithography technique using ArF excimer laser (wavelength of 193 nm). The photolithography techniques using light, however, have been approaching their limits. EUV lithography technique using EUV (at a wavelength of 13.5 nm) has been attracting attention as a new lithography technique after the ArF immersion lithography. In the semiconductor device production process using EUV lithography, a substrate coated with an EUV resist is exposed by EUV radiation and developed to form a resist pattern.
An overlayer on an EUV resist is described, which includes a polymer including a group containing one or more of beryllium, boron, carbon, silicon, zirconium, niobium, and molybdenum in order to protect the EUV resist from contaminants and to block undesirable radiation, for example, such as UV and DUV (Out of Band/out-of-band radiation, OOB) (Patent Document 1, Patent Document 2).
There are examples in which, in order to block OOB, a topcoat formed of a polyhydroxystyrene (PHS)-based compound, an acrylic compound, or other substances is applied as an overlayer on an EUV resist to reduce OOB (Non Patent Document 1), or a film of an EUV resolution enhancement layer is applied as an overlayer on an EUV resist to absorb OOB and improve the EUV resist resolution (Non Patent Document 2). However, what composition is most suitable is not described. A novolac-based material including a naphthalene ring is described as a resist overlayer film forming composition for EUV lithography (Patent Document 3).
Resist overlayer protective films that have hydrophobicity suitable for immersion lithography and can be dissolved in an aqueous alkaline solution are disclosed as follows: a resist protecting film material including an acrylic polymer including a hexafluoroisopropyl alcohol group (Patent Document 4); a resist protecting film material including an ester compound having a fluoroalkyl group as a solvent (Patent Document 5); a photoresist overlayer film forming composition including a solvent having an ether structure (Patent Document 6); and a topcoat material including a hexafluoroalcohol unit and an alcohol-based solvent, which can be used as a topcoat for immersion process or a top anti-reflective coating (TARC) to be applied on the top surface of a photoresist (Patent Document 7).
However, it is unclear whether these materials have sufficient characteristics as resist overlayer films particularly for use in EUV lithography that can transmit EUV light and block OOB radiation and as materials excellent at blocking gas escaped from the resist.